In a large mixing bowl, beat together butter and sugar.

Add egg, milk and vanilla, mix well.

In a separate bowl, whisk together flour, cocoa powder, baking soda and salt.

Add flour mixture to butter mixture,stirring with spoon until well combined and no more dry patches.

Refrigerate dough for 1 -2 hours or until chilled and firm enough to handle. Dough will be a little soft.

Preheat oven to 350°F. Lightly grease cookie sheet or line with parchment paper.

Scoop out tablespoon of cookie dough. Roll dough into a ball. Flatten slightly and press peppermint patty into dough. Mold dough around patty so that it is completely covered. It's important that the patty is completely covered - it will melt and ooze out if it's not.

Place on prepared cookie sheet.

Bake for about 12 minutes or until cookie is set.

Let cookie rest for a minute or two on cookie sheet and carefully transfer to wire rack. Cool completely. Store in sealed container.

Makes approximately 18 cookies.